A welding mask usually comprises facial protection means allowing the operator's face or part of his face, to be protected from possible splashes of materials, the facial protection means being provided with holding means allowing the welding mask to be held in position on the operator's head.
The scene of the welding carried out by the operator is viewed through a window made within the facial protection means, which window is generally fitted with a tinted glass allowing the radiation emitted by the electric arc during the welding operation proper to be attenuated.
There are many grades of tinted glass allowing the light radiation to be attenuated to a greater or lesser extent, the grade to be used therefore depending on the task to be accomplished and increasing with the welding current.
Furthermore, this type of mask fitted with tinted sheets of glass therefore allows the operator, on the one hand, to see the arc and the weld pool and, on the other hand, to protect the operator from the light radiation emitted by the electric arc, namely ultraviolet, infrared and/or visible radiation.
There are also liquid-crystal helmets or masks for which the tinted glass is replaced by a cassette composed of a liquid-crystal matrix sandwiched between two polarizing sheets of glass.
These masks especially have the advantage of allowing the desired level of attenuation to be adjusted, either automatically or manually.
These two types of mask allow the operator to observe the welding scene only in the visible, i.e. from the visible radiation emitted or reflected by the welding scene.
However, in the visible spectrum, the welding arc is the main source of illumination and it follows that the radiation which emanates therefrom is predominant compared with all the other potential sources of illumination.
In other words, it is difficult to distinguish, through these conventional-type masks, anything else other than the electric arc itself and those parts of the welding scene illuminated by the electric arc, namely essentially part of the weld pool and of its immediate environment.
Thus, it is almost impossible with these masks of the prior art to distinguish the zones located near the weld pool but beneath the arc, as well as any possible transfer of material likely to occur in the electric arc itself.